Process for the manufacture of urea from cyanamide



pas ed m 24, 1927.

UNITED STATES PATENT 1 OFFICE.

' i JOSEPH BRESLAUER AND CHARLES GOUDET, F GENEVA, SWITZERLAND, ASSIGNORS TO SOGIE'IE DETUDES CHIMIQUES POUR LIHDUSTRIE,

A COMPANY OF SWITZERLAND.

01E GENEVA, SWITZERLAXD,

rnocnss son THE MANUFACTURE or UREA mom cYANAMmE.

- There are many different methods of converting cyanamide into urea. For nstance this substance is generally treated with acid catalyzers to facilitate the addition of a 6 molecule of water, The treatment of the cyanamide with acids under pressure has also been already patented. I

. All hitherto known processes have certain drawbacks for instance the following ones:

1. Whenthe cyanamide is treated with the acid catalyzers under ordinary pressure, it is necessary to employ a certain amount of acid, for instance sulphuric acid, to' obtaina rapid conversion and to avoid the formation of polymerized products which always appear after a certajn time.

According to the researches made, it 1s advisable to employ a quantity of acid corresponding to about per 'cent -of the quantity theoretically necessary for obtainin the complete conversion of the urea into so phate of urea, or other salt of-ureadepending upon the acid employed. However it is impossible to employ less than 15 per cent of this quantity without prolonging in a dangerous manner the durw tion of the operation and Without diminishing the output of urea, and increasing the amount of dieyandiamide and other polymerized products. I

2. When'the process is carried on under pressure (for lnstance according to the process of Immendorf & Kappen) at a temperature of 110 to 120 centigrade as it is described in the German Patents No's.

257,642 and 257 ,643, about the same result is obtained. Even in employing greater uantities of acid Messrs. Immendorf &

appen according to their patents, have not- 40 succeeded in converting more than 80 pr cent of cyanamide into urea. But it ought to be pointed out that this quantity is determined in an indirect manner by diluting the sulphate of ammonium, and that quite s6 arbitrarily it isassuied that the rest is urea.

shown that by proceeding according to the f method of Immendorf"& Kappen a yield is obtained which is much lowerthan that mentioned in'their patent and that the final productnot only consists of sulphate of amin Drawin Application'filed lanuary 27, 1923, Serial No. 615,315, and m Switzerlandlebruary 4, 1922.

monium and urea but contains polymers of cyanamide the amount of which varies according to the method employed.

Applicants have found that it-is possible to obtain the desired result; that, is, a nearly quantitative conversion of cyanamide into urea which is technically purewhile diminishmgthe quantity. of acids employed as catalyzers, when certain conditions of term perature and pressure are observed;

The present invention relates to a process temperature less than 7 5, degrees centi rude and at a pressure above the atmos acid catalyzerin a quantity less than 10 per cent of the quantity of acid theoretically necessary for the fi zation of the Whole urea as'a'salt of urea.

The acid. catalyzer may be an acid such for instance as sulphuric, phosphoric, nitric tioned abov Experiments which show it is possible to convert the whole quantity of the nitrogen of the cyanamlde contained in the solution 'into urea, determined by the xanthydrol,

have proven that for each concentration of cyanamide and a determined uantity of sulphuric acid, there exist conditions of. temperature, and of duration of heating, which are to be found in eachcase by experiment.v

Moreover it has been stated that from an economlcal point of view, it is advantageous p to use solutions of cyanamide, which ar a The experlments madeby applicants have i s concentrated as possible.

Exam le: A S0ll1t10ll0f free cyaiiamide prepare by treating 1 kg. calcium cyanamide suspended in water with carbon diox-' for the manufacture of urea from cyanamide (H GN which consists in treating at a' eric prcssure, a solution of cyanamide wlth an tit y t dilute acid. The solution pbtained is poured into an autoclave the total nitrogen contained in the solution of cyanamide employed.

he described process ofl'ers, with re rd to the hitherto known pI0CeSSS,'th8 f0 owing advantages: 1 v Owing to thesimplicity oi the. operations and the small quantity of acid employed, 'it is possible to manufacture from calcium cy;

anamide, urea in a form which may be employed for agricultural purposes.

The small quantities of. sulphuric acid which remain in the urea may either be converted into calcium sulphate by the carbomate of calcium and incorporated into the technical urea, or serve for the conversion of ":a small quantity of tricalcium phosphate In both the cases it is also into bior monocal'cium phosphate by means of the processes belonging to us and described 1n other patent specifications. ible to separate by filtrationthe insolub e sulphate or phosphate from the solution of urea and to employ separately the substances obtained thereby.

It is to be noted that the e ense of acid may be considered as nil and t at the process opens an unlimited field to the pre aratlon of manures from calcium cyanami e.

We claim as our invention: 1. A process for the manufacture of urea from cyanamide consisting in treating a solution ofc anamide' at a temperature of approximate y 70 C. and at a pressure approximating 7 atmospheres by antacid catalyzer in a. quantity less than 10% of the quantity of acid necessary for the'fixation of the whole urea as a salt of urea.

2. A process for the manufacture of urea from cyanamide consisting in treating a concentrated solution of cyanamide at a temperature of approximately 70 C. and at a pressure approximating 7 atmospheres by an acid cata yzer less in quantity than 10% of the quantity of acid necessary for the fixation of the whole quantity of urea as a salt of urea.

3. A process for the manufacture of urea from cyanamide consisting in treating a solution of c anamide at a temperature of approximate y 7 0 degrees centlgrade and undera pressure of approximately 7 atmospheres by an acid catalyzer in aquantity approximating 5 per cent of the quantit of acid necessary for the fixation of the w ole quantity of urea as a salt of area.

In testimonywhereof we haveafi'ixed our signatures. v

'- Da. JOSEPH BRESLAUER.

DB. CHARLES GOUDET. 

